Production of magnesium



Aug 3 3141321 to z Aug. 3 1926. 1,594,344

H. E. BAKKEN PRODUCTION OF MAGNESIUM Original Filed Nov. 1, 1922' 2 Sheets-Sheet 2 Patented Aug. .3, 1926. I i

UNITED sTATEs PATENT OFFICE.

HERMAN E. BAKKEN, OI NIAGARA FALLS, NEW YORK, ASSIGNOR EEO-AMERICAN MAG- NESIUM CORPORATION, OF NIAGARA FALLS, NEW YORK, A CORPORATION OI' NEW YORK.

PRODUCTION OF MAGNESIUM.

Application filed November 1, 1922, Serial No. 598,292. Renewed April 17, 1926.

. My invention relates to the production in the condenser is slightly less than themof metallic magnesium in a substantially por pressure of the magnesium at the tem- 65 chemically pure state. By the processes perature of the solid metal being sublimed. that are at present practiced, magnesium Under these conditions, the evolution of i 6 when produced from ores containing other magnesium vapor will be rapid and if metals and metalloids, is likely to be conproper condensation facilitaties are protaminated with them. For use in the mevided the rate of sublimation is only limchani'cal arts, these impurities must be reited by the'rate at which heat can be supmoved as it is found that they exert a plied to the metal being sublimed. This 1 marked influence on the physical and chemipoint at which the vapor pressure of the solid cal properties of the metal when present in magnesium becomes greater than the absoonlya very limited degree. lute pressure of the system is hereinafter My process is particularly adapted for use called the sublimation point. in refining crude metal. It is applicable al- By virtue of operating at or above the sub- 15 so to obtaining pure metal from magnesium limation point I do not only produce rapid scrap, such as castings, alloys, etc. sublimation, but by the rush of magnesium y invention comprises the purification vapor toward the condenser I sweep out and 7 of magnesium by converting the solid metal away the residual amount of air or other directly into the state of vapor and then congas in the apparatus, and thus reduce Very densing it directly in-the solid state without much the tendency of this gas to combine intermediate liquefaction, and in particular with the magnesium and render the product it consists in the discovery of suitable means impure.

and conditions whereby such purification can One of the great advantages of my method be made practically operable and capable of of sublimation as compared with vacuum being commercially carried out so as to prodistillation of magnesium is that not on} duce pure magnesium at a reasonable cost. can it be made to be as rapid as the distil- It is known that magnesium boils at atlation but it also gives a considerably purer mospheric pressure at about 1120 C. Puriproduct. In vacuum distillation I have fication by distillation at this temperature, found that no matter how carefully the dishowever, is in practice very diflicult because tillation is carried on, there is always a cerof the fact that the necessary apparatus detain proportion of non-volatile or substantcriorates rapidly at suchahigh temperature. tially non-volatile impurities, carried over By reducing the pressure in the apparatus, into the condensed metal. I ascribe this i. e. by carrying on the distillation under phenomenon to the well-knowm-tendenoy of diminished pressure, the boiling point of. gases or vapors to carry with themminute the metal can be reduced, until it coincides droplets or spray of any liquid thru which with the melting point at a pressure of apthey pass or from which they are evolved,

proximately 2 millimeters of mercury, thus particularly if they are evolved rapidly. This reducing the difliculty found in producing spray of impure magnesiumcarried over suitable apparatus of a suificient size to hanfrom the boiling liquid contaminates the disdle commercial quantities of metal, and tillate, but its formation appears to be prestrong enough to satisfactorily withstand the vented by subliming rather than distilling continued external pressure involved. the magnesium so as to avoid the phenom- I have discovered, however, that if the enon of the evolution =of bubbles from a pressure inside the apparatus is still further liquid.

reduced, say to less than about 1 mm., rapid It will be apprehended that the process sublimation of the magnesium may be. acis capable of being carried out in a number complished at temperatures which are withof difierent types of apparatus and that the in the range where ordinary steel apparatus one shown and described is merely illustrawill function satisfactorily. In order to ob tive of the principles of the invention. This tain rapid sublimation, it is necessary to so embodiment, however, has been found to be adjust or regulate the operating pressure to practical in construction and operation and a point where the total absolute presssure eificient in use.'

Referring to. the drawings for a more complete disclosure of the invention:

Figure l is a vertical longitudinal section of the furnace;

Figure 2 is a section on the'line 2-2 of Figure 1;

Figure 3 is a detail ofthe cover and closing mechanism for the retort;

Figure 4 is a section on the line 4-4 of Figure 1;

The iron retort 1 is suitably supported and inclosed in a brickwork and may be heated by burners projecting through the openings 2 and 3 in the lower corners of the combustion chamber, or in any other suitable manner. The retort at itslower ends is supported by the vertical brick wall 5 and by the wall collar 6. Intermediate its ends, it is supported by a wall collar 7 carried by the center wall 8 and at its front end by the wall collar 9 carried by the front wall 10. In such aconstruction, the greater part of the retort is in the zone of heat, the remainder extending out into the air to provide a cold end therefor, which may be provided with cooling coils.

tity of crude, impure, or alloyed ma The charging end of the retort is closed by a, suitable door 11 which is so constructed as to make the same as gas tight as possible. A suitable construction comprises lugs 13 integral with the retort and a series of hooks 20 welded to the lugs and clamped between the bars 14 of theframework 15. Carried between the said bars are screw blocks 16 which engage with the screws 17 of the hand wheels 18. Rotation of the said wheels in suitable direction will loosen or tighten the cover of the retort.

For determining the temperature at the bottom of the retort a pyrometer well 19 is provided and a similar pyrometer well 21 is provided at the top of the retort.

For facilitating removal of the deposited crystals a liner 22 is located in the cooler end of the retort.

This liner consists of a pipe somewhat smaller than the inside diameter ,of the retort, so that it can be easily slipped in and taken out. The liner is open at both ends, and at its lower end rests on the annular ring 23, integral with the pot, the other end extending up to the closing flange. The purpose of the ring 23 is to keep the liner from slipping down into the retort and also to form a seal so that gaseous magnesium does not travel up between the liner and the retort wall. The liner may be made in one piece or split longitudinally into two halves, golfacilitate removal of the deposited crys- (Operation.

The pot is charged with a suitable quanesium,

sealed and vacuum applied. on the nae-wee vacuum has been obtained, heat is applied,

care being taken to maintain the vacuum. After a suitable period of time, the temperature will rise to about 600 degrees C. and is held there for about 5 or 6 hours. At the end of that time, the source of heat is cut 0d and the retort allowed to cool while still under the same vacuum.

Under the conditions outlined, the magnesium does not melt but passes directly from the solid into the vapor state. The vapor passes into the cooler portion of the retort where it condenses on the liner. When opened, the inner surf-ace of the liner will be found to be covered with crystallized magnesium which can be removed in a suitable manner. Analysis of the residue in the bottom of the retort will show that nearly all the magnesium has been vaporized. Analysis of the crystals of magnesium will show that the magnesium content may be as high as 99.989%.

The best available data indicate that the vapor pressure of magnesium decreases from one atmosphere or 760 mm. of mercury at 11 20 0., which is ordinarily spoken of as its boiling point, to approximately 2 mm. at

its melting point, 651 C. Below the melting point the vapor pressure gradually decreases, so that after a further drop of about 270 C. it is still about 0.001 mm. If crude, impure or alloyed magnesium is heated at a temperature below its melting point, the magnesium will vaporize so as to produce a partial pressure of magnesium vapor, determined by the temperature. If this heating is done in the presence of an inert gas such as argon, at atmospheric pressure or under diminished pressure, but still at a total pressure greater than the vapor pressure of magnesium at the temperature employed, this magnesium vapor will diifuse thru the inert gas; and if another part of the apparatus is cooler than the metal being heated, magnesium will gradually condense in this ortion of the apparatus. This rate of sublimation is so slow, however, that I have found it very advantageous to reduce the total pressure within the condenser to a point below the vapor pressure of the magnesium at the temperature employed, as

measured at 19, Fig. 1. Instead of having to slowly diffuse thru the inert gas present, the magnesium vapor will then. be rapidly evolved at a suficient pressure to sweep this gas away and into the condenser; where, by a suitable regulation of the condenser temperature, I continuously condense this va- -porin the form of a very pure crystalline to this difference in temperature is the drivlng force causing the rapid'transfer of the magnesium vapor from the subliming to the condensing end of the system. This difference in pressure must be equal to the sum of the partial pressure of the inert gas present in the condenser and the pressure required to overcome the frictional resistance and force the vapor from the subliming to the condensing end. The importance of these factors is seen by the fact that calculation shows that if magnesium be sublimed in an apparatus such as the one shown in Fig. 1, having a cross-sectional area of one square foot at the section 4- 1, at a temperature of 600 C. and a pressure of 0.75 mm the linear velocity of the magnesium vapor which would be necessary to sublime 100 pounds of magnesium in 24 hours would be in excess of onehalf mile a minute. Diffusion, such as would take place if the total pressure within the apparatus were greater than the vapor pressure of magnesium at the temperature employed, is known to take place relatively slowly, and it' is evident that my method of sublimation of magnesium will be much more rapid than one which depends upon diifusion. The temperature of sublimation and converselyof solidification may vary from approximately 300 degrees at 0.001 mm. pressure to 651 degrees at approximately 2 mm. pressure; The most favorable operating conditions at the present time have been found to be a temperature of approximately 600 degrees C. and a pressure of 0.5-0.2 mm. Under such conditions I am able to sublime 100 pounds of magnesium in 4 hours in an apparatus having a cross section of approximately one square foot.

The crystallized metal can be handled in different ways. It can be placed in an extrusion press and extruded of the customary structural wire, bars, tubes, rods etc. The crystals can also be compressed into briquets at a temperature of about 200 degrees C. and give a substantially chemically pure metal in a marketable form. This might not be shapes, such as irectly into any the case if themetal were firstmelted and cast, on account of the fact that oxides and nitrides would be introduced into the metal by melting. This metal is also highly resistant to corrosion due to its extreme purity.

' I claim 1. In a method of producing pure magnesium, the step comprising subjecting material containing metallic magnesium to an absolute pressure less than the vapor pressure of magnesium at its melting point, and heating the said material to its sublimation point to cause the magnesium to vaporize rapidly.

2. The method of producing pure magneslum comprising su jecting material containing metallic magnesium to an absolute pressure less than the vapor pressure of magnesium at its melting point, heating the said material to the sublimation point and thereafter reducing the temperature of the evolved vapor to cause solidification of the magnesium.

3. The method of producing refined magnesium comprising subjecting impure magnesium. to such temperature and pressure as will cause the magnesium to sublime rapidly.

4. The method of producing refined magnesium comprising subjecting impure mag nesium in a solid form to a temperature not less than about 300 degrees C. and to an absolute pressure less than about 2 mm. of mercury to vaporize the metal and bringing the vapors in contact with a surface, the temperature of which is substantially lova er than the melting pointof magnesium to cause solidification oi the magnesium in the form of crystals. V

5. The method of refining impure magnesium comprising subjecting the metal to a temperature between approximately 300 degrees C. and its freezing point and to an absolute pressure of approximately 0.001 to 2 mm.

In testimony whereof I aifix my signature.

HER AN E. BAKKEN. 

